1. Field of the Invention
The invention relates to artificial intraocular lens implants for the phakic or pseudophakic human eye.
2. Description of the Prior Art
It is well known that there are many ways the human eye can deviate from the optical ideal of emmetropia, in which images are precisely focused on the retina naturally, without assistance or effort, resulting in clear vision requiring no additional optical correction. Such deviations from the optical ideal of emmetropia which produce an optically non-ideal situation, or ammetropia, include:
1. Myopia (near-sightedness)--in which the image of the object of regard is focused in front of the retina producing a blurry image on the retina itself.
2. Hyperopia (far-sightedness)--in which the image of the object of regard is focused behind the retina producing a blurry image on the retina itself.
3. Astigmatism (asymmetry or irregularity of corneal curvature)--producing an irregular and therefore blurry image.
4. Presbyopia--loss of the accommodative ability of the naturally occurring human crystalline lens, making near objects blurry.
5. A combination of the above.
The presence of these optically aberrant or ammetropic conditions is due to a relative mismatching of the optical powers of the optical elements of the eye (primarily the cornea and lens) with respect to the position of the retina, which produces a failure of the eye as an optical system to function in the desired manner to give clear vision. This can occur in spite of the otherwise normal condition of the tissues of the optical elements involved.
Many methods have been developed in an attempt to correct the above mentioned group of naturally occurring ammetropic conditions of myopia, hyperopia, astigmatism, and presbyopia including:
1. Spectacle correction--in which refracting lenses in glasses frames are positioned in front of the eye, external to, and not in contact with the cornea.
2. Contact lenses--which physically rest upon the external surface of the cornea and its tear film and alter the overall optical status of the eye by means of their refractive optical power and also by the physical presence on the corneal surface thereby neutralizing irregularities of the corneal surface. A technique known as orthokeratology has been developed in which the shape of the cornea is modified by fitting a contact lens having a particular desired curvature which is intended to change the shape of the cornea to the curvature of the contact lens. This technique has had minimal success due to the nonpermanent nature of the induced curvature change on the cornea by the contact lens, and is practiced little today.
3. Refractive surgery--in which the optical refractive status of the eye is altered through some surgical procedure. One general group of procedures is referred to as corneal refractive surgery in which a change in the corneal shape, or refractive index, or both, is surgically induced, thereby changing the corneal optical power. Examples of corneal refractive surgery are:
A. Radial keratotomy--(developed initially by Sato in Japan in 1939 and more recently popularized by S.N. Fyodorov in Russia and brought to the U.S. by Bores) in which radial incisions are made into the substance of the corneal tissue changing its shape. This procedure, along with many variations in the orientation, length, number and depth of incisions, has been used to correct myopia, astigmatism, and more recently hyperopia.
B. Keratophakia (originated by Jose Barraquer--Bogota, Colombia) and its variations such as epikeratoplasty (developed by Kaufman and MacDonald) --in which properly preshaped human donor tissue is surgically placed on the external surface of the cornea, thereby altering the overall corneal shape and consequently its refractive effect.
C. Keratomileusis--(originated by Barraquer, Colombia)--in which the patient's surface corneal tissue is removed, reshaped in some fashion at surgery, and replaced on the corneal surface in its new configuration.
D. Synthetic corneal onlay--in which a synthetic material (silicone or hydrogel-like material) is placed directly onto the corneal surface, thereby altering the corneal shape.
E. Synthetic corneal inlay--(developed by Peter Choyce)--in which a pocket is surgically developed within the layers of the corneal tissue into which is slid or placed a polysulfone disc which, by its higher refractive index than the surrounding normal corneal tissue, alters the overall optical power of the cornea. Note U.S. Pat. No. 4,624,669. Another type of corneal inlay procedure is also under development notably by Dr. Theodore Werblin in which the surface corneal tissue is removed centrally and a refractive disc (which is made of synthetic silicone-like or hydrogel-like materials)is placed within this bed, after which the previously removed corneal tissue is replaced over the inlay. The inlay is consequently "sandwiched" between the previously removed anterior corneal surface tissue in front and the posterior corneal tissue behind, and has its effect, unlike the inlay of Choyce, primarily by means of changing the corneal curvature.
F. Corneal laser sculpting--in which by means of the application of laser energy (notably currently eximer laser energy) to the corneal tissue, the cornea is reconfigured by means of incisions (as in radial keratotomy) or reshaped (sculpted) to alter its configuration.
Another general type of refractive surgery has been directed toward altering the length of the eye by means of scleral resection or support, generally intending to shorten the anterior/posterior ocular length in long, highly myopic eyes. This surgery is extremely complex, dangerous, and generally ineffective and has fallen into disuse.
A different surgical approach in highly myopic eyes has been recently advocated by Verzella in which the clear (noncataractous) lens is removed, leaving the eye aphakic. Because of the loss of the optical converging power of the naturally occurring human lens, the eye is rendered less myopic. Some have advocated the removal of the natural lens and replacement with an intraocular lens of less convergent power, which also makes the eye less myopic.
Cataract removal, particularly with the advent of intraocular lenses, must technically also be considered a type of refractive surgery. However, it differs considerably from the previously described procedures in that the eye, specifically the optical element--the human lens, is not normal, but is cataractous. The eye may in fact be otherwise emmetropic. The cataract surgery is performed expressly for the purpose of removal of the cataract for vision improvement. The intraocular lens is implanted for optical correction of the eye which now requires optical correction only because the cataractous lens has now been removed.
Also, technically, the surgery of keratoprosthesis implantation is a refractive procedure in which an optical element with a surrounding stabilizing element is implanted (imbedded actually) in the tissue of the cornea into which it finally becomes an integral part. This procedure, however, is reserved for the most desperate of situations in which usually the corneal tissue is markedly scarred and opaque and there is little if any hope of successful visual rehabilitation with any other surgical approach.
Another surgical procedure for altering the refractive status of the ammetropic usually myopic but otherwise healthy, phakic eye has been the implantation of an intraocular lens within the phakic eye, virtually exclusively in the anterior chamber. This particular location has been used in order to avoid physical contact between the intraocular lens and the normal human lens which might result in traumatic damage to the human lens and possibly cataract formation. In the late 1940's and early 1950's, when this type of procedure was first attempted, complications from these anterior chamber implants such as chronic inflammation within the eye (iritis), corneal swelling and cloudiness, glaucoma, and cataracts did indeed occur. These complications were the result both of poor intraocular lens designs (which resulted in implant being too close to the cornea, particularly peripherally, and to the human lens centrally), materials and manufacture. The complication rates of these early anterior chamber implant procedures were so high and the results were so poor that the procedure was abandoned.
With our improved understanding of intraocular lens biopathology, lens designs, materials and manufacturing techniques, the procedure of anterior chamber intraocular lens implantation in phakic eyes has recently been resurrected with modern anterior chamber intraocular lens implants. These phakic implants have been implanted virtually exclusively in the anterior chamber to avoid the previously mentioned complications of iritis, corneal swelling and decompensation, glaucoma, and especially cataract, all of which as mentioned, have been encountered before. The anterior chamber is the location which affords the greatest separation between the implanted intraocular lens and the human lens. This principle of maximum separation between the intraocular lens implant and the human lens has been reinforced by the recent development of anterior chamber implants for refractive correction of phakic eyes which have a greater anterior vault or angulation than anterior chamber implants used for cataract surgery. This greater angulation, however, has the considerable disadvantage of placing the implant closer to the cornea risking corneal touch with resultant damage, eventual swelling and decompensation.
A final method of refractive correction in the phakic eye has been described by Mazzocco (U.S. Pat. No. 4,573,998) Blackmore (U.S. Pat. No. 4,585,456), and Kelman (U.S. Pat. No. 4,769,035) in which it is proposed that the optically corrective device be placed directly on the crystalline lens of the eye. This general concept of placement of the optical device directly upon the crystalline lens places the implant as far as possible from the delicate structures of the cornea, specifically the endothelium, which is a distinct advantage over phakic implants placed in the anterior chamber. The particular design of Mazzocco specifically addresses a method of implantation comprising a series of steps including an intraocular lens having a deformable optical portion which must be compressed to about 80% or more of the cross-sectional diameter prior to insertion into the eye. The compressible implant is described as having various mechanisms of fixation, which include: 1. Suturing to the iris anteriorly by means of a suture passed through the iris and through openings located in the periphery of the implant device (FIGS. 9, 10, 21, 21a, 22, 22a in the Mazzocco U.S. Pat. No. 4,573,998), or 2. By means of peripheral fixating members which hold the implant in position through physical contact and pressure upon the tissues of the periphery of the eye, either in the anterior chamber in the angle (FIGS. 11, 12, 15-20, 23,24, 25, 26 in the Mazzocco U.S. Pat. No. 4,573,998 ), or more pertinent to the discussion here, in the posterior chamber, peripheral to the lens and posterior to the iris in the ciliary sulcus (FIG. 60 in Mazzocco patent). Therefore, although the proposed optically corrective implant devices of Mazzocco are proposed to lie upon the human crystalline lens, they obtain their fixation from a location other than the human crystalline lens, namely the angle (anterior chamber), iris, or the ciliary sulcus (posterior chamber). Note also Blackmore (U.S. Pat. No. 4,585,466) and Kelman (U.S. Pat. No. 4,769,035).
To summarize, the corneal refractive procedures are;
1. Incisional reshaping (surgical knife or laser)--such as radial keratotomy. PA0 2. Corneal onlays. PA0 3. Corneal inlays. PA0 4. Laser corneal reshaping. PA0 5. Keratoprosthesis implantation. PA0 6. Scleral resection--no longer widely used. PA0 7. Lensectomy PA0 8. Phakic IOL implantation--uses anterior chamber IOL (modified with greater anterior vault) PA0 9. IOL placed on the anterior surface of the iris or anterior surface of the lens and held in position by peripheral fixation members.
A. Human donor tissue--keratophakia, epikereatoplasty. PA1 B. Reshaped patient's tissue--keratomileusis. PA1 C. Synthetic material. PA1 A. Polysulfone--refractive index change effect. PA1 B. Silicone or hydrogel--configuration change effect (mainly). PA1 A. Clear lensectomy (either alone or with implantation of a low power IOL) PA1 B. Cataract extraction with IOL implantation.
With particular reference to the compressible IOL described by Mazzocco, it should be noted that the various mechanisms of fixation he proposes for stabilization of the implant (anterior chamber angle, iris and ciliary sulcus) are well known to be less biocompatible (and therefore less acceptable) when they have been utilized for fixation of intraocular lenses which have been implanted after cataract extraction. It is reasonable for anyone skilled in the art to deduct from this previous clinical experience with intraocular lenses implanted after cataract extraction, that these mechanisms of fixation would be similarly less bicompatible and therefore less desirable in any intraocular lens implant device placed within the eye directly upon the crystalline lens.
This is a particular concern since it is anticipated that surgical optical refractive correction would be attempted in a patient population generally considerably younger than the population in which cataract extraction is common. Therefore, it would be expected that a younger patient would require a longer lifetime of intraocular acceptance from such an implant. This increased lifetime expectancy puts an even greater demand on any phakic implant design to be maximally biocompatible, and a crucial feature of any phakic implant design is its fixation mechanism. A maximally biocompatible fixation mechanism is essential to ensure long-term ocular acceptance of any phakic implant. Clearly, the more rigorous design requirements of a phakic implant eliminate the previously proposed fixation mechanisms of Mazzocco, Blackmore, and Kelman of anterior chamber angle, iris, or ciliary sulcus fixation as acceptable options. Unfortunately, the fixation mechanism which has been found to be most biocompatible for intraocular lenses implanted after cataract extraction, namely, fixation within the capsular bag, is not available for phakic implant fixation since the human crystalline lens remains intact.
This overall situation, therefore, leaves the questions of a suitably biocompatible fixation mechanism for a phakic implant which physically rests partially or completely on the human crystalline lens unanswered by the prior art.